The recent sinking of a South Korean naval vessel by North Korea is not an attack by North Korea on South Korea. It is an attack on the United States by China.
Obama is seen as a wimp world wide, someone who will not use force until pushed into a corner and even then will capitulate to unreasonable demands rather than continue the hawkish international politics of his predecessor.
The Chinese are testing the ability of the Obama administration to react to overt military action against a loyal ally. The Chinese are depending on Obama seeking a peaceful and political solution to a public disgrace.
In the end the Chinese will get what they want. Obama will not defend South Korea which will pretty much destroy the political relationship between the United States and South Korea. South Korea will turn to China.
Eventually so will Japan.
Obama could do a lot of things and even deny responsibility the way Carter used to. This would put a lot of political pressure on China and North Korea.
Obama will pussy out and this will be the start of an eventual east-west confrontation which will leave China in political control of most of the world.